Postprandial glucose, insulin, and glucagon-like peptide-1 responses of different equine breeds adapted to meals containing micronized maize1

Abstract

The enteroinsular axis is a complex system that includes the release of incretin hormones from the gut to promote the absorption and utilization of glucose after a meal. The insulinogenic effect of incretin hormones such as glucagon-like peptide-1 (GLP-1) remains poorly characterized in the horse. The aim of this study was to compare postprandial glucose, insulin, and GLP-1 responses of different equine breeds adapted to twice-daily meals containing micronized maize. Four Standardbred horses, 4 mixed-breed ponies, and 4 Andalusian cross horses in moderate BCS (5.5 ± 0.2 out of 9) were fed meals at 0800 and 1600 h each day. The meals contained micronized maize (mixed with soaked soybean hulls and lucerne chaff), with the amount of maize gradually increased over 12 wk to reach a final quantity of 1.7 g/kg BW (1.1 g/kg BW starch) in each meal. Animals had ad libitum access to the same hay throughout. After 12 wk of acclimation, serial blood samples were collected from all animals over a 14-h period to measure concentrations of glucose, insulin, and GLP-1, with meals fed immediately after the 0 and 8 h samples. Glucose area under the curve (AUC) values were similar between breed groups (P = 0.41); however, ponies and Andalusian horses exhibited significantly higher insulin AUC values after both meals compared with Standardbred horses (both P < 0.005). Postprandial GLP-1 AUC values were also significantly higher in ponies and Andalusian horses compared with Standardbred horses (breed × time interaction; P < 0.001). Correlation analysis demonstrated a strong positive association between concentrations of insulin and GLP-1 over time (rs = 0.752; P < 0.001). The increased insulin concentrations in ponies and Andalusian horses may partly reflect lower insulin sensitivity but could also be attributed to increased GLP-1 release. Given that hyperinsulinemia is a recognized risk factor for the development of laminitis in domestic equids, this study provides evidence that the enteroinsular axis warrants further investigation.

Repeatability of Oral Sugar Test Results, Glucagon‐Like Peptide‐1 Measurements, and Serum High‐Molecular‐Weight Adiponectin Concentrations in Horses

“…Both aGLP‐1 and tGLP‐1 concentrations had wide 95% CIs (−8.68 to 7.86 pM and −8.52 to 6.77 pM) when Bland‐Altman analyses were performed. Lower plasma aGLP‐1 concentrations were detected in the MO‐ID group, compared to the MO‐N group, which was surprising because aGLP‐1 stimulates insulin secretion and higher concentrations were expected in horses and ponies with ID . In a study previously performed by our research group, aGLP‐1 concentrations were higher (but not significantly) during the OST in EMS horses, when compared with normal horses .…”

“…Another study also detected higher plasma aGLP‐1 concentrations in hyperinsulinemic ponies when oral glucose tests were performed . Breed of horse has been shown to affect aGLP‐1 concentrations, with ponies and Andalusian horses reaching higher concentrations during oral glucose tests than Standardbred horses . A strong positive correlation ( r s = 0.752; P < .001) between insulin and aGLP‐1 concentrations was reported in the same study.…”

The repeatability of an oral glucose test in ponies

“…Postprandial hyperinsulinaemia, particularly after a meal high in nonstructural carbohydrates (NSC), appears to be a hallmark of insulin dysregulation [7,8] and this may or may not be exacerbated by peripheral insulin resistance (IR), as measured by the i.v. The intake of grain-based diets and/ or forage/pasture can be associated with consumption of NSCs at a level that causes significant and/or persistent hyperinsulinaemia [8,10]. The intake of grain-based diets and/ or forage/pasture can be associated with consumption of NSCs at a level that causes significant and/or persistent hyperinsulinaemia [8,10].…”

“…The intake of grain-based diets and/ or forage/pasture can be associated with consumption of NSCs at a level that causes significant and/or persistent hyperinsulinaemia [8,10]. Incretin hormones augment insulin release from the pancreas, and upregulation of the enteroinsular axis has been implicated in equine insulin dysregulation [7,8,11]. Incretin hormones augment insulin release from the pancreas, and upregulation of the enteroinsular axis has been implicated in equine insulin dysregulation [7,8,11].…”

Repeatability of the hyperglycaemic clamp for assessment of β‐cell response and insulin sensitivity in horses

“…Horses with ID are predisposed to laminitis and excessive hyperinsulinaemia has been linked to laminitis in several studies . The β‐cells modulate insulin secretion depending on factors such as the degree of insulin sensitivity (IS) , the level of hyperglycaemia and incretin effects . How all these factors contribute to the excessive postprandial hyperinsulinaemia in ID horses is incompletely understood.…”